This invention relates generally to textiles useful in industrial products. In one aspect, the invention relates to heavy duty textile fabrics, specifically geotextile fabrics, and high impact bags made from woven fabric such as explosive bags and intermediate bulk containers.
There are many industrial uses of textiles which require fabrics of high strength and durability. These fabrics and/or textiles, referred to as industrial textiles, are distinguished from apparel and household textiles on the basis of denier: the industrial textiles employ heavy denier yarns with emphasis on strength and durability whereas the apparel and household textiles employ low denier yarns with emphasis on esthetics.
Many of the industrial textiles are in the form of woven or knitted fabrics made from synthetic tape yarns. Such yarns are extruded flat tapes (or films) woven into the fabric in a flat, untwisted disposition. The flat configuration of the tape yarns provide relatively large area coverage in comparison to round yarns, but still retains the tensile strength in proportion to its cross sectional area. Tape yarns are used as the fill and warp yarns in both woven and knitted fabrics.
Although tape yarns have received considerable use in industrial textiles such as geotextiles, and high impact fabric bags, they present certain operational problems and suffer certain deficiencies, particularly in fabrics that are stitch bonded or needle punched. For example, polypropylene tapes are used as the fill and warp yarns in woven geotextile fabric. These fabrics are joined together by stitching overlapped edge portions of the fabric. More recently, multilayers of fabrics are joined by stitch bonding to produce a geotextile of excellent strength. Also, intermediate bulk containers and explosive bags are frequently fabricated by sewing components together.
It has been discovered that needle penetration in such sewing or stitching operations damage the flat tape yarns to the extent that the tensile strength of the fabric is substantially reduced. Examination of the damaged tape yarns reveals that the needle penetration causes fibrillation (splitting) of the yarn generally in a random direction. Although the tape yarns are oriented in the machine direction (MD), the tape splits caused by needle penetration do not usually propagate in the MD but instead extend in random directions. This not only produces many loose-ended fibrils but also reduces the effective cross-sectional area of the tape and hence its tensile strength. Tests on commercial polypropylene tape yarns have shown that needle penetration reduces yarn tensile strength on an average of 25%, reaching 50% on some samples. Tests on geotextile fabrics stitch bonded together has shown reduction in tensile strength of the final composite by as much as 40% in comparison to tensile strength of the composite without stitch bonding.
Another serious problem associated with flat yarns is their lack of flexibility with respect to the longitudinal axis of the yarn. Tape yarns are rectangular in cross section having a thickness to width ratio (aspect ratio) of between about 1:10 to 1:40. Such flat yarns, because of their thinness, are extremely flexible for winding up and bending around MD curves. However, the relatively narrow width tape is resistant to bending from side-to-side or about its longitudinal axis. Thus, any forces tending to cause the tape to fold along its longitudinal axis will create high stress sites. This stress, coupled with the sharp edges of the tape, results in equipment wear on circular guides or other components which restrict lateral movement of the yarn during textile fabrication. Moreover, in certain weaving operations, such as in circular weaving, the high tensions maintained on the yarns during the weaving operation cause the sharp edges of the circumferential yarns (fill) to damage the longitudinal yarns (warp) to the extent that yarn breakage is a problem.
As described in detail below, the present invention overcomes many of the problems associated with flat tape yarns by using a tape yarn composed of a plurality of rounded filaments arranged in parallel relation and being integral with adjacent filaments. The prior art includes many references which disclose tape yarns of diverse cross sections intended for a variety of uses. For example, U.S. Pat. Nos. 3,164,948, 3,273,771, 3,470,685, 3,495,752 and British Pat. No. 1,202,347 disclose flat tapes comprising individual monofilaments joined by bridges. The purpose of the relatively thin bridges is to aid in promoting fibrillation of the tape. Fibrillation, as the name implies, is a process for forming fibers by splitting the film in the MD. The fibrillated tapes are twisted to form a bundle of fibrils joined at longitudinal intervals. The relatively narrow bridges of the prior art tape permit controlled fibrillation of the tapes prior to or during twisting or working in forming the multifilament yarn. Although the fibrillation improves the appearance and flexibility of the yarns, their use in the twisted bundle sacrifices the principal advantages of flat tape--large surface areas.